Saturday, April 11, 2015

ECG Blog #108 (Ventricular Rhythms - AIVR - VT)

NOTE: This is the "short version" of my ECG Blog #107 — in that I only address the 3-lead rhythm strip shown below (which was Figure-3 in Blog #107)

The simultaneously-recorded 3-lead rhythm strip shown in the Figure was obtained from a 69-year old woman with a longterm history of palpitations. Her symptoms had been increasing over recent weeks, in association with "chest tightness" and dizziness. Her prior medical history was benign  and she was hemodynamically stable at the time this tracing was recorded.
  • How would you interpret the rhythm shown in the Figure?
  • What are clinical implications of this rhythm

Figure: Simultaneously-recorded 3-lead Rhythm Strip, obtained from a 69-year old woman with palpitations. She was hemodynamically stable at the time of this tracing. What is the rhythm? What clinical implications are associated with this rhythm? 

Interpretation: The rhythm is fairly regular — albeit with slight variation in rate.
  • The QRS complex is wide (at least 3 little boxes = ≥0.12 second in duration).
  • Normal sinus P waves are missing in lead II. Instead, there are retrograde (negative) P waves that are clearly seen to occur after the QRS in lead II (RED arrows).
  • The rhythm is AIVR (Accelerated IdioVentricular Rhythm) — which is a slower form of ventricular tachycardia.
  • NOTE: The finding of 1:1 V-A (ie, retrograde) atrial activity is not "AV dissociation" — because these retrograde P waves are related to the QRS complex. When there is AV dissociation — then P waves are not related to neighboring QRS complexes.

Discussion: AIVR is an "enhanced" ventricular ectopic rhythm that occurs faster than the intrinsic ventricular escape rate (which is ~20-40/minute— and slower than hemodynamically significant Ventricular Tachycardia (ie, VT at rates >130-140/minute).
  • The usual rate of AIVR is therefore between ~60-110/minute (with an area of "overlap" between AIVR and fast VT at ~110-130/minute).
  • PEARL #1 AIVR generally occurs in one of the following Clinical Settingsi) as a rhythm during cardiac arrest; ii) in the monitoring phase of acute MI (especially with inferior MI); oriii) as a reperfusion arrhythmia (following thrombolysis, acute angioplasty, or spontaneous reperfusion). It may also occur in patients with underlying coronary disease, cardiomyopathy, and with digoxin toxicity. 
  • AIVR is often an "escape rhythm" — in that it arises because both the SA and AV nodes are not functioning. IF treatment is needed (because loss of the atrial "kick" results in hypotension) — Atropine is the drug of choice (in hope of speeding up the SA node to resume its pacemaking function). AIVR should not be shocked nor treated with antiarrhythmic medication such as Amiodarone/Procainamide — since doing so might result in asystole.

PEARL #2 On rare occasions — AIVR may occur intermittently in otherwise healthy subjects without underlying heart disease. If such subjects are asymptomatic during episodes — then no treatment is needed. NOTE: When AIVR occurs in otherwise healthy individuals (often in athletes) — it is usually due to increased vagal tone that is able to exert its influence on the ectopic ventricular focus (See Riera reference below).
  • KEY Point: The importance of distinguishing between AIVR (ie, "slow VT" )vs "fast VT" (heart rate generally ≥130/minute) — is that active treatment of AIVR is usually not needed (provided the patient is hemodynamically stable and tolerating the rhythm) — whereas the opposite is true for sustained VT. Instead — "benign neglect" ( = observation) is often the most prudent course of action (in addition to ensuring adequate oxygenation, normal electrolytes, etc.) for AIVR — since this form of ventricular rhythm is far less likely to deteriorate to fast VT/VFib. 
  • As we have already noted — there is an intermediate ( = "gray zone" ) rate range when the ventricular rhythm is in between ~110-130/minute, for which clinical judgment is needed (depending on the scenario) for determining whether active treatment of the ventricular rhythm is likely to be needed.
We do NOT know why the patient in this case presented with runs of AIVR (possibly for a period of years ... ). Recent or remote ischemia/infarction and cardiomyopathy should be ruled out. The possibility of SSS (Sick Sinus Syndrome) — with emergence of AIVR as an escape rhythm should also be considered as part of the work-up. Unfortunately — We have no follow-up ...

ACKNOWLEDGMENT: My appreciation goes to Sam Walker (from Auckland, New Zealand) for allowing me to use this case and these tracings. 

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  1. Sometimes it is difficult to distinguish AIVR from Hyperkalemia with sinus arrest with sine waves. Any comments on this sir?

    1. @ Dr. Rahul — Exactly! That said, the clinical scenario will often provide the BEST clue (until serum K+ comes back from the lab). THANKS for your comment — :)